In spectroscopic methods, it is conventional to perform spectral measurements on a system by letting through a luminous beam transmitted or sent back by this system through a slit. Scanning the slit then enables to cover a selected spectral domain.
The noise generated in the signals obtained is thus rather penalising, and obliges generally to implement different filtering techniques to obtain satisfactory results. The noise includes in particular a component with rapid fluctuations, i.e. over a small wavelength scale with respect to the bandwidths of the peaks of the signals (in particular smaller than one fifth of the bandwidths), and a low fluctuation component, i.e. over a great wavelength scale with respect to the bandwidth of the peaks (in particular 5 times greater). This second component of the noise includes notably a background noise, consisting of spurious intensity level, added to that of the signals.